Most mainstream distributions, like Ubuntu, Fedora, and Mandriva, have already adopted a time-based release schedule, meaning that releases are not done on a feature basis, but according to a pre-determined time schedule. The Debian project has announced that it has adopted a time-based release schedule too.

I'm an active Debian user (20 servers on Lenny and 10 workstations on Testing) and having more predictability is always good for planning. And Lenny -> StableAfterNext upgrade promise is wise move.

Although I must admit that planning a freeze in 4 months is pretty radical - many important upgrades (kernel, x.org, etc) have still not reached to Squeeze and it still looks a lot like Lenny (with the exception of DE - KDE, Gnome and Xfce have all been upgraded).